1. Field of the Invention
The present invention relates to non-destructive testing and evaluation and, more particularly, to a system for in-situ detection and monitoring of corrosion in structures with the ability to directly track the presence and growth of corrosion on a structure by measurement of material loss in the structure.
2. Description of Background
Structural health monitoring systems aim to diagnose flaws in components to prevent catastrophic degradation and failure. The benefit of such a system is the ability to determine the need for replacement of a structural component. This need often arises as a result of corrosion damage.
Corrosion damage is of significant concern across all engineering fields. Corrosion damage to vehicle components (aerospace, naval, and land vehicles) is the predominant form of damage and limits the useful life of structures and their components. Corrosion consists of an electrochemical interaction between materials which gradually degrades the material over time. Structural components which undergo the corrosive process lose material and, as a result, exhibit lowered structural integrity. The loss of structural integrity increases the likelihood of failure of the part. Coatings exist which aim to prevent corrosion by providing a barrier for the electrochemical interaction involved in the corrosive process. However, the best outcome when using coating techniques is a delay in the onset of corrosive damage on systems in the field. Wear and tear experienced by systems in the field reduces the efficacy of such coatings. Thus corrosion monitoring systems are still necessary for fielded systems.
Significant effort, in the form of manpower and monetary resources, is required for diagnosing corrosion damage and replacing parts. Since corrosion damage is closely linked to operational environment and use, conventional predictions of corrosion damage to structural components are speculative. Therefore, there is a significant industrial demand for a more reliable diagnostic system for corrosion monitoring and growth tracking, since this would save significant manpower and costs associated with corrosion damage. Such a corrosion monitoring system would reduce the costs associated with maintenance and also reduce total life cycle costs. These savings are significant, especially when extended to a fleet of systems such as air or ground vehicles.
Existing corrosion monitoring techniques can be classified into three main categories. The first category consists of sensor implementations that rely on sacrificial materials that corrode along with the base substructure on which the sensor is mounted. For example, U.S. Pat. No. 5,367,583 describes a technique based on fiber optics which uses a sacrificial element. The second category consists of sensors and techniques that monitor low level electric potentials and electric currents which indicate the presence of a corrosion process. For example, U.S. Pat. No. 5,139,627 describes a sensor system which measures the electric current related to corrosion. The third category is based on sensor techniques which measure the chemical properties of the environment for factors conducive to corrosion formation. As an example, U.S. Pat. No. 5,306,414 describes a technique that measures chemical species in the environment.
Other forms of non-destructive testing and evaluation have been used in other contexts. For example, techniques based on in-situ smart materials for structures have been used for health monitoring. In-situ sensors and actuators are used to excite a structure using high frequency vibrations and advanced algorithms are used for damage detection. For example, U.S. Pat. No. 6,006,163 describes a system using piezoelectric transducers and broadband excitation for damage detection of structures. U.S. Pat. No. 6,799,466 describes a system using electromagnetic acoustic transducers for pipeline monitoring.
To the best of the present inventor's knowledge, there have been no known efforts at corrosion monitoring by direct monitoring of the structure as opposed to the use of sacrificial elements, measurement of electric potentials and currents, or environmental properties conducive to corrosion. It would be greatly advantageous to provide a system with the ability to directly track the presence and growth of corrosion on a structural system by relying on guided waves to directly measure material loss, rather than relying on conventional methods which have inherent drawbacks.
Other features, advantages and characteristics of the present invention will become apparent after the following detailed description.